1. Field of the Invention
This invention relates to coated ink jet recording media suitable for use in making film laminates and film laminates thereof. The ink jet recording media are coated with compositions comprising alumina hydrate particulate and are capable of providing recorded images having good image quality, waterfastness, and lightfastness.
2. Brief Description of the Related Art
In recent years, large format ink jet printers have been used to manufacture large color-printed media, such as graphic art indoor and outdoor advertising displays. The large format ink jet printers impart high loadings of ink onto an ink jet recording medium having an ink-receptive coating on its surface.
Since large-format printed media are often displayed indoors or outdoors, the printed medium should possess good water-resistance, smear-resistance and image quality. Most ink jet recording media are coated papers or coated polymeric films, and the ink-receptive coatings thereon usually contain water-soluble or water-swellable polymers. Thus, recorded images on these ink-jet recording media usually have poor water-resistance and smear-resistance. Previous attempts have been made at developing ink jet media to provide recorded images with good image quality, waterfastness, and lightfastness.
For example, Cousin et al., U.S. Pat. 4,554,181 describes coating an ink jet recording sheet with a coating comprising a cationic polymer and a water-soluble polyvalent metal salt to improve image quality, waterfastness, and feathering. Representative cationic polymers are described as homopolymers or copolymers of cationic monomers such as quaternary diallyldialkylammonium chlorides. The coating composition may also comprise a water-swellable polymer binder such as polyvinyl alcohol, polyacrylates, polymethacrylates, or poly(vinyl pyrrolidone).
Furukawa et al., U.S. Pat. No. 5,439,739 describes an ink jet recording medium capable of providing recording images having excellent water-resistance, which is obtained by coating a support with a coating containing a water-soluble polymer and a cross-linking agent. The water-soluble polymer is made by copolymerizing a quaternary salt monomer, an amino group-containing monomer or a carboxyl group-containing monomer, and a monomer selected from acrylarmine, 2-hydroxyethyl (meth)acrylate, and N-vinylpyrrolidone. The coating composition may also contain water-soluble polymers such as polyvinyl alcohol, starch, carboxymethyl cellulose, and cationized gelatin. Inorganic pigments such as alumina sol and cationic colloidal silica and polymer particles such as micron-size polystyrene fine particles can be added to the ink-receiving layer.
Williams et al., U.S. Pat. No. 5,494,759 discloses ink jet printing materials comprising a support and an ink receiving layer containing a pigment, a hydrophilic binder comprising a mixture of polyvinylalcohol, polyvinylpyrrolidone, and a vinyl acetate homopolymer and/or vinyl acetate alkyl acrylate copolymer, and a quaternary ammonium compound.
Published Japanese Pat. Kokai 91,981/92 (Mitsubishi Paper Mills, Ltd.) describes a paper cast-coated with a dispersed mixture of silica, a cationic resin, (polydiallyldimethylammonium)chloride, and a binder resin, (polyvinyl alcohol).
Ink jet recording media that have been color-imaged can be used to make film laminates by laminating a layer of transparent polymeric film over the printed image. The polymeric film protects the printed image and gives the image a glossy appearance. Basically, there are two different types of laminate films that can be applied to color-imaged media. One type of laminate film is a pressure-sensitive, adhesive-coated polymeric film. This laminate film can be laminated onto a color-imaged medium at room temperature and is commonly referred to as a xe2x80x9ccold laminate filmxe2x80x9d. Another type of laminate film is a hot-melt, adhesive-coated polymeric film. This type of laminate film must be laminated onto a color-imaged medium at a temperature of 180xc2x0 F. to 270xc2x0 F. and is commonly referred to as a xe2x80x9chot laminate filmxe2x80x9d. Usually, cold laminate films can be laminated onto any color-imaged medium, because the soft and tacky pressure-sensitive adhesive-coating on the laminate film sticks to any imaged surface. However, hot laminate films often do not stick well to color-imaged surfaces, because the absorbed dyes in the ink-receptive coating reduce the adhesion of the hot laminate film to the imaged surface. In such instances, the hot laminate film can delaminate from the imaged medium during subsequent handling.
In view of the foregoing problems with many ink jet recording media, it would be desirable to have a medium capable of providing images having good image quality, waterfastness, smear-resistance, and lightfastness. The medium should also be capable of being laminated with films, particularly hot laminate films, after the medium has been color-imaged. The present invention provides such ink jet recording media.
The present invention provides an ink jet recording medium comprising a substrate and two ink-receptive coating layers. The first ink-receptive layer comprises a water-soluble polymer and alumina hydrate particulate, and the second ink-receptive layer comprises a blend of water-soluble polymers, wherein at least one of the blended polymers is a quaternary amine-containing polymer. The second ink-receptive coating is coated on the first ink-receptive coating.
The substrate is a paper or polymeric film. Suitable polymeric film substrates include, for example, vinyl, polyethylene, polypropylene, polycarbonate, polyimide, polyester, and fluoroplastic films. The polymeric film may be opaque. Suitable paper substrates include, for example, plain paper, clay-coated paper, resin-coated paper, latex-saturated paper, and polyethylene-coated paper. Preferably, polyethylene-coated paper is used.
The first ink-receptive coating layer contains a water-soluble polymer such as, for example, gelatin, polyvinyl alcohol, polyvinyl pyrrolidone, poly(2-ethyl-2-oxazoline), or mixtures thereof Typically, the alumina hydrate particles have a surface area of about 100 to about 200 m2/g and an average dispersed particle size of about 40 to about 200 nm. Preferably, the first ink-receptive coating layer comprises about 10 to about 60 dry wt. % of alumina hydrate particles and about 40 to about 90 dry wt. % of poly(2-ethyl-2-oxazoline) and has a thickness of about 5 to about 50 xcexcm.
The second ink-receptive coating layer contains a water-soluble polymer such as, for example, polyvinyl alcohol, polyvinyl pyrrolidone, or poly(2-ethyl-2-oxazoline) blended with a quaternary amine-containing polymer. Preferably, the quaternary amine-containing polymer is a quaternized vinyl pyrrolidone/dimethylaminoethylmethacrylate copolymer. The second ink-receptive coating may also contain a transitional metal salt such as, for example, a water-soluble copper (II) or cobalt (III) salt, particularly copper (II) sulfate, copper (III) acetate, or cobalt (III) acetate and additives such as optical brighteners and pigments. Preferably, the second ink-receptive coating layer has a thickness of about 0.1 to about 10 xcexcm.
In a preferred ink jet recording medium of this invention, the bottom layer comprises poly(2-ethyl-2-oxazoline) and alumina hydrate particulate, while the top layer comprises a copolymer of vinyl pyrrolidone and quaternized dimethylaminoethylacrylate, stilbene-based optical brightener, and poly(methyl methacrylate) pigment.
This invention also encompasses film laminates comprising transparent polymeric films and the above-described ink jet recording media. The transparent films are laminated to the second ink-receptive coating layers of the media after the media have been imaged. Suitable transparent polymeric films for laminating onto the imaged media include vinyl, polyethylene, polypropylene, polycarbonate, polyimide, polyester, and fluoroplastic films.
The present invention relates to an ink jet recording medium comprising a substrate and two ink-receptive coating layers. By the term xe2x80x9csubstratexe2x80x9d, it is meant any suitable paper or polymeric film that can be treated with the coating layers. For example, papers can be chosen from plain papers, clay-coated papers, resin-coated papers (e.g., polyethylene-coated paper) or latex-saturated papers. In the present invention, a polyethylene-coated paper is preferably selected as the substrate, based on its good handling and coating characteristics. Polymeric films can be chosen from vinyl, polyethylene, polypropylene, polycarbonate, polyimide, polyester, polyethylene terephthalate or fluoroplastic films. The thickness of the substrate is not limited and may be selected according to the particular applications of the medium.
The above substrates have two surfaces. The first surface, which is coated with an ink-receptive coating, is called the xe2x80x9cfront surfacexe2x80x9d, and the opposite surface is called the xe2x80x9cback surfacexe2x80x9d or underside. The chosen substrate may be pretreated, if so desired, by conventional techniques. For example, when the chosen substrate is a polymeric film substrate, a surface treatment, such as corona discharge or a primer coating, may be applied to one surface or both surfaces thereof. For a resin-coated paper substrate, the front and back surfaces may be treated by corona discharge. If a primer coating is used, the coating typically comprises a polymeric resin such as polyester, acrylic, epoxy, polyurethane, or the like, with polyurethane being preferred.
The front surface of the substrate, i.e., imaging surface, is pretreated so that it will adhere better to the ink receiving coating. The back surface, i.e., non-imaging surface, is pretreated in order to provide an adhesion promoting layer for a backing material. A backing material such as a polymeric resin, polymeric film, or paper may then be placed on the back surface in order to reduce electrostatic charge, sheet-to-sheet friction and, and curl of the substrate.
In the present invention, the front surface of the chosen substrate is coated with a two-layer ink-receptive coating. The first (i.e., bottom) ink-receptive layer is designed to absorb ink solvents and the second (i.e., top) ink-receptive layer is designed to absorb dyes found in the ink. The bottom layer is also designed to provide good adhesion to the front surface of the substrate, while the top layer is also designed to provide good adhesion to a laminate film after the top layer has been imaged.
The bottom ink-receptive coating layer comprises a water-soluble polymer resin and alumina hydrate particles. The water-soluble polymer resin in the bottom layer may be chosen from any suitable water-soluble polymer resin such as gelatin, polyvinyl alcohol (PVOH), polyvinyl pyrrolidone (PVP), polyvinyl acetate (PVA), polyethylene oxide (PEO), poly(2-ethyl-2-oxazoline) (PEOX), and mixtures thereof. In the present invention, PEOX and blends containing PEOX are preferred when the substrate is a polyethylene-coated paper, because PEOX adheres well to the paper, even when the front surface of the paper does not have a primer coating.
It is important that alumina hydrate particles be used in the bottom ink-receptive layer in order to obtain good adhesion between the various components in a laminate film product, particularly between the imaged ink-receptive layers and paper substrate. If silica, calcium carbonate, titanium dioxide, or clay particles are used in the bottom layer, then the imaged layers may poorly adhere to the paper substrate resulting in delamination problems. Further, the alumina hydrate particles must be blended thoroughly with the water-soluble polymer to achieve a uniform coating. Preferably, the alumina hydrate particles are incorporated into the coating layer by adding an alumina sol to the water-soluble polymer. If the mixture containing the alumina hydrate particles and water-soluble polymer is not vigorously stirred so that the particles and polymer are thoroughly blended together, the mixture tends to form a gel. Since it is difficult to uniformly coat the gel onto the paper substrate, the bottom ink-receptive layer in such media products is usually discontinuous and non-uniform. When media products having such non-uniform coatings are color-imaged, the color density and quality tends to be poor.
Preferably, the alumina hydrate particles have a surface area of 100 to 200 m2/g and an average dispersed particle size of 40 to 200 nm. The content of the alumina hydrate particles in the bottom ink-receptive layer is preferably from 10 to 150% by dry weight based on the weight of the water-soluble polymeric resin in the bottom layer. If the content of the particulate exceeds 150% by dry weight of the polymeric resin, the bottom layer tends not to effectively adhere to the paper substrate.
In the present invention, the top ink-receptive coating layer comprises a blend of water-soluble polymers. At least one of the water-soluble polymers in the blend is a quaternary amine-containing polymer. It is important that the quaternary amine-containing polymer be water-soluble to allow more dye molecules to interact with the quaternary amine-containing polymer. Although the quaternary amine-containing polymer is water-soluble, the cationic groups in the polymer are still capable of reacting with and stabilizing the anionic dyes contained in the ink. If a non-water soluble quaternary amine-containing polymer is used, more dye molecules tend to remain on the surface of the coating layer and these molecules do not interact with the quaternary amine-containing polymer. In preparing the blend of water-soluble polymers for use as the top coating layer, the water-soluble quaternary amine-containing polymer can be blended with the same water-soluble polymer resin used for the first ink-receptive (bottom) layer, or it can be blended with a different water-soluble polymer resin. It is preferred that the water-soluble quaternary amine-containing polymer be blended with a water-soluble polymer selected from the group consisting of PVOH, PVP, and PEOX. It is further preferred that the water-soluble quaternary amine-containing polymer be a copolymer of vinyl pyrrolidone and quaternized dimethylaminoethylacrylate (such as commercially available Gafquat(copyright), from ISP Technologies, Inc.). In this respect, a copolymer of vinyl pyrrolidone and quaternized dimethylaminoethylacrylate is preferred because it gives a glossy and flexible coating which can also fix dyes in the top ink-receptive layer.
The top ink-receptive coating layer may also contain a transitional metal salt. If a transitional metal salt(s) is used in the top layer, it is water-soluble and preferably chosen from the group consisting of copper sulfate, copper acetate, and cobalt acetate. Copper sulfate is especially preferred because it is inexpensive and widely available. The transitional metal ions in the top layer help to stabilize dyes and greatly increase the light-fastness of the ink receiving coating. The content of the transitional metal salt (e.g., copper sulfate) is preferably from about 0.1% to about 20% by dry weight of the water-soluble polymeric resin(s) in the top layer.
Pigments, and optical brighteners, and other conventional additives such as UV blockers/stabilizers, and surface active agents can also be used in the top ink-receptive coating layer, depending on the intended application of the ink jet recording medium. Examples of suitable pigments include polyolefins, polystyrene, starch, polyurethane, poly(methyl methacrylate) (such as Soken(copyright) MR10G, available from Espirit Chemical Company), polytetrafluoroethylene (such as Shamrock SST2SP5, available from Shamrock Chemical Company), and the like. Examples of suitable optical brighteners include stilbene-based and distyryl biphenyl-based optical brighteners such as those available in the Tinopal(copyright) series from Ciba-Geigy.
In a preferred ink jet recording medium of this invention, the bottom ink-receptive layer comprises poly(2-ethyl-2-oxazoline) and alumina hydrate particulate, while the top ink-receptive layer comprises a copolymer of vinyl pyrrolidone and quaternized dimethylaminoethylacrylate, poly(vinyl alcohol), stilbene-based optical brightener, and poly(methyl methacrylate) pigment.
The ink jet recording media of this invention are particularly useful for making laminate films, where a transparent polymeric film is laminated onto the top ink-receptive layer and underside of the substrate after the medium has been imaged, i.e., printed. Conventional techniques can be used to make the laminate films. Preferably, the film is laminated onto the imaged medium by a pressure-sensitive or hot-melt adhesive. Suitable transparent polymeric films that can be laminated onto the imaged medium include vinyl, polyethylene, polypropylene, polycarbonate, polyimide, polyester, and fluoroplastic films.
The invention is further illustrated by the following examples using the below test methods, but these examples should not be construed as limiting the scope of the invention.
Adhesion of Imaged Coating to Laminate Film
In some of the following examples, the adhesion of the imaged coating (i.e., the ink-receptive coating containing an image) to a laminate film was measured by a peel strength tester used in the pressure-sensitive adhesive industry. A substrate coated with the ink-receptive layers of the present invention was imaged on a particular printer with a particular ink set and printed with a test pattern comprising (xe2x85x9e inch wide, about 10 inch long) color stripes (yellow, cyan, magenta, blue, green, red and black) described in further detail in the following examples.
After the printed color stripes were dried, a plain paper stripe one inch wide was placed perpendicularly on top of the color stripes, and then the printed substrate was laminated between two layers of hot laminate film on a laminating machine at a temperature ranging from 180xc2x0 F. to 270xc2x0 F. The laminated medium was then cut in the direction of the plain paper strip down the middle of the plain paper stripe, so that the laminate film on the image side could be lifted for testing. The laminate film on each color was cut into a xe2x85x9c inch width stripe (in the middle of the printed stripe area). The laminate film was then peeled off from the imaged area and the peel strength was measured with a 3M 90 Slip/Peel Tester (Instrumentors, Inc.).
Lightfastness
Ink jet image colors fade under exposure to sunlight. The commonly used coordinate system for color is the CIE-L*a*b* system. In order to quantitatively measure the lightfastness, L*a*b* values are measured before (initial L*a*b* values) and after (final L*a*b* values) the samples are exposed to sunlight. xcex94E=((Lf*xe2x80x94Li*)2+(af*xe2x80x94ai*)2+(bf*xe2x80x94bi*)2)xc2xd. xcex94E is a measure of the color difference between the faded and unfaded colors. Samples and colors having poor lightfastness have larger xcex94E values. The values of L*a*b* were measured with a X-Rite 918 0/45 Colorimeter (X-Rite, Inc.).
The lightfastness of the laminated, imaged samples was determined by exposing the samples to sunlight over a period of two weeks in the summer. The laminated, imaged samples were exposed to sunlight by taping them to the outside surface of an office window. In some instances, the lightfastness of the samples was determined by manually observing the samples before and after being exposed to sunlight. In other instances, the L*a*b* values of the samples were measured before and after being exposed to sunlight and the xcex94E of the samples was calculated as described above.